Nicotine is found predominantly in the genus Nicotiana and in low quantities in some other species of the family Solanaceae (Sheen S J (1988) J Food Science 53: 1572-1573). Nicotine is the most abundant alkaloid in commercial tobacco (N. tabacum L.) cultivars (Siminszky et al. (2005) Proc Natl Acad Sci USA 102: 14919-14924), and naturally plays an important role in tobacco resistance to insect herbivores (Steppuhn et al (2004) PLoS Biology 2: 1074-1080). Nicotine is synthesized in tobacco root tip and transported to leaf and stored in leaf cell vacuole by a multidrug and toxic compound extrusion (MATE) transporter (Morita et al. (2009) Proc Natl Acad Sci 106: 2447-2452). The pathway for nicotine biosynthesis involves convergence of two biosynthetically distinct branches. The enzymes and the genes encoding these enzymes involved in the pathway have been identified except for the enzyme/gene that catalyzes the final condensation step of nicotinic acid and methyl-pyrrolinium cation to form nicotine, generally referred to as nicotine synthase. It has been proposed that a reduction reaction occurs followed by oxidation of nicotinic acid prior to formation of specific pyridine moiety that condenses with the methylpyrrolinium cation to form nicotine (Friesen and Leete (1990) Tetrahedron Letters 31:6295-6298). A622 and NBB1 have been proposed as catalysts of the final steps of nicotine biosynthesis (Hibi et al. (1994) Plant Cell 6:723-35: Shoji et al. (2002) Plant Mol Biol 50:427-440; Hashimoto and Kato 2007; Kajikawa et al. (2009) Plant Mol Biol 69: 287-298; Kajikawa et al. (2011) Plant Physiol 155(4):2010-22). Putrescine N-methyltransferase (PMT) and quinolinic acid phosphoribosyltransferase (QPT), the first committing enzymes in each branch of the nicotine biosynthetic pathway, are believed to be the key enzymes in nicotine production (Feth et al. (1986) Planta 168: 402-407; Wagner et al. (1986) Physiol Plantarum 68: 667-672). A few minor alkaloids, including nornicotine, anabasine, and anatabine, are also synthesized in this pathway, with nornicotine being directly converted from nicotine by nicotine demethylase whose corresponding genes have been cloned (Siminszky et al. (2005) Proc Natl Acad Sci USA 102: 14919-14924).
This invention addresses the need for compositions and methods that modulate the nicotine biosynthesis pathway in plants.